winter active bees
© UnknownWarmer winters have led to bumblebees remaining active throughout the winter months.
It is one of the sounds of summer, but now the buzz of the bumblebee is becoming increasingly familiar in deepest winter - at a time when the insects should be hibernating.

Scientists are investigating the growing phenomenon of bumblebees remaining active throughout the winter months.

They believe it is a consequence of recent warmer winters, linked to climate change, as well as the British passion for gardening and the increasing popularity of exotic, winter flowering shrubs from which bees can collect food.

Another theory being explored is that the bees may be hybridising with foreign bees, which remain active in winter, and which may have escaped into the wild after being imported into Britain to help with the pollination of crops in polytunnels.

The phenomenon has been recorded in the buff-tailed bumblebee (Bombus terrestris), one of the most common in the UK. Like other bees, it is usually only seen between March and September as it spends autumn and winter asleep underground, but there have been increasing reports of winter activity in recent years.

The dramatic change in the insect's lifestyle is now being monitored by scientists at Queen Mary, University of London (QMUL) and the Bees Wasps and Ants Recording Society, as part of a research project funded by the Leverhulme Trust.

Dr Thomas Ings, from the university, who has been carrying out the study with Marc Carlton and Ralph Stelzer, said: "Some people think you are mad when you talk about bees in the winter, but we seem to see this happening quite a lot now. We need to find out what is going on."

The trend is most noticeable in the south east and west of England, although last winter - when winter bee activity was recorded at almost 600 sites - there were sightings in East Anglia, Wales, the Midlands and as far north as Hull.

The winter bees seem to be an entirely urban or suburban phenomenon, as they forage on garden plants, particularly Mahonia, a shrub native to Asia as well as North America but now popular in British gardens.

Colonies monitored in London suggest that foraging rates for the bees in winter can be even greater than in the summer - meaning that they are able to get lots of food.

"Preliminary data collected by Marc Carlton shows that there is a second cycle active during the winter," Dr Ings added. "It doesn't seem to be the bees extending their life from the summer and lasting longer into the autumn. They are starting all over again in the winter."

Traditionally, the queens go into hibernation in protected places such in soil or under moss, from late July or August. They then emerge in March, as the weather warms, with each queen starting up her own colony, where she lays eggs.

Worker bees hatch and take on the nectar and pollen gathering role. The queen lays more eggs, which become males and new queens for the next year.

The old queen then dies with from exhaustion from the end of July onwards, while the younger queens go into hibernation.

Now, scientists believe that the queens emerge from a "mini hibernation", in October and start foraging once more, setting up a nest, laying eggs and starting the process all over again. The next generation of queen bees are produced in February or March - about the time they would expect to come out of hibernation.

There are some reports that another species, the early bumblebee (Bombus pratorum) is also attempting to remain active during the winter.

The dramatic change in the life cycle of the bee comes as many species are under threat in the UK and scientists believe it could be an encouraging sign of how they are able to adapt to climate change.

However, there are fears it could leave the species vulnerable, as a large proportion could be wiped out by extreme cold snaps.

It could also have a detrimental effect on other species, if they are not able to adapt so well, as they could lose out on scarce resources to the more successful buff-tailed bumblebee.

Prof David Goulson, from the Bumblebee Conservation Trust and an academic from Stirling University, said: "The real puzzle is that it is not just a climate change thing. It doesn't happen in Brittany, for example, or anywhere else in the world.

"If you go to France, you won't find these winter-active bees. My guess is that it is also to do with the British passion for gardening and the number of exotic, winter-flowering plants that you now find."